Kuenzel Wayne J, Kang Seong W, Zhou Z Jimmy
Department of Poultry Science, University of Arkansas, Fayetteville 72701
Department of Poultry Science, University of Arkansas, Fayetteville 72701.
Poult Sci. 2015 Apr;94(4):786-98. doi: 10.3382/ps.2014-4370.
In the eyes of mammals, specialized photoreceptors called intrinsically photosensitive retinal ganglion cells (ipRGC) have been identified that sense photoperiodic or daylight exposure, providing them over time with seasonal information. Detectors of photoperiods are critical in vertebrates, particularly for timing the onset of reproduction each year. In birds, the eyes do not appear to monitor photoperiodic information; rather, neurons within at least 4 different brain structures have been proposed to function in this capacity. Specialized neurons, called deep brain photoreceptors (DBP), have been found in the septum and 3 hypothalamic areas. Within each of the 4 brain loci, one or more of 3 unique photopigments, including melanopsin, neuropsin, and vertebrate ancient opsin, have been identified. An experiment was designed to characterize electrophysiological responses of neurons proposed to be avian DBP following light stimulation. A second study used immature chicks raised under short-day photoperiods and transferred to long day lengths. Gene expression of photopigments was then determined in 3 septal-hypothalamic regions. Preliminary electrophysiological data obtained from patch-clamping neurons in brain slices have shown that bipolar neurons in the lateral septal organ responded to photostimulation comparable with mammalian ipRGC, particularly by showing depolarization and a delayed, slow response to directed light stimulation. Utilizing real-time reverse-transcription PCR, it was found that all 3 photopigments showed significantly increased gene expression in the septal-hypothalamic regions in chicks on the third day after being transferred to long-day photoperiods. Each dissected region contained structures previously proposed to have DBP. The highly significant increased gene expression for all 3 photopigments on the third, long-day photoperiod in brain regions proposed to contain 4 structures with DBP suggests that all 3 types of DBP (melanopsin, neuropsin, and vertebrate ancient opsin) in more than one neural site in the septal-hypothalamic area are involved in reproductive function. The neural response to light of at least 2 of the proposed DBP in the septal/hypothalamic region resembles the primitive, functional, sensory ipRGC well characterized in mammals.
在哺乳动物眼中，已鉴定出一种名为内在光敏视网膜神经节细胞（ipRGC）的特殊光感受器，它能感知光周期或日光照射，随着时间推移为它们提供季节性信息。光周期探测器在脊椎动物中至关重要，特别是对于每年繁殖开始的时间安排。在鸟类中，眼睛似乎并不监测光周期信息；相反，至少4种不同脑结构中的神经元被认为具有此功能。在隔区和3个下丘脑区域发现了一种名为深部脑光感受器（DBP）的特殊神经元。在这4个脑区中的每一个区域，都已鉴定出3种独特光色素中的一种或多种，包括黑视蛋白、神经视蛋白和脊椎动物古老视蛋白。设计了一项实验来表征被认为是鸟类DBP的神经元在光刺激后的电生理反应。第二项研究使用了在短日照光周期下饲养并转移到长日照光周期的未成熟雏鸡。然后在3个隔区 - 下丘脑区域测定光色素的基因表达。从脑切片中对神经元进行膜片钳记录获得的初步电生理数据表明，外侧隔器官中的双极神经元对光刺激的反应与哺乳动物的ipRGC相当，特别是通过显示去极化以及对定向光刺激的延迟、缓慢反应。利用实时逆转录PCR发现，在转移到长日照光周期后的第三天，所有3种光色素在雏鸡的隔区 - 下丘脑区域的基因表达均显著增加。每个解剖区域都包含先前被认为具有DBP的结构。在被认为包含4个具有DBP结构的脑区中，所有3种光色素在长日照光周期的第三天基因表达高度显著增加，这表明隔区 - 下丘脑区域中不止一个神经部位的所有3种类型的DBP（黑视蛋白、神经视蛋白和脊椎动物古老视蛋白）都参与生殖功能。隔区/下丘脑区域中至少2种被认为是DBP的神经元对光的神经反应与在哺乳动物中得到充分表征的原始、功能性感觉ipRGC相似。
